An electronic device configured as an environmental sensor may include a sensor integrated circuit (“IC”) die, enclosed within the cavity of a cavity-type package. To enable the sensor IC die to sense particular characteristics of the environment, the package may include an opening (e.g., through the package lid) that permits exposure of the sensor IC die to the external environment. In some types of sensors, a protective material (e.g., a gel) may be disposed inside the cavity and covering the sensor IC die, in order to protect the sensor IC die from otherwise potentially destructive exposure to the external environment. In some types of devices, the quantity of gel disposed within the cavity is selected so that an air gap is present between the surface of the gel and the package's lid. If, for example, the sensor IC die is configured to sense environmental pressure, during such a pressure sensing operation, the force of air pressure impinging upon the exposed surface of the gel is translated through the gel to a sensing element (e.g., a transducer) implemented in the pressure sensor IC die. The pressure sensor IC die transducer then generates an electrical signal indicative of the pressure imposed. A non-limiting example of such a pressure sensor transducer is a piezo-resistive transducer (“PRT”) pressure sensor.
In some cases, moisture entering the package cavity may result in reliability and/or accuracy issues for such sensor devices. For example, moisture may diffuse through the relatively-permeable, protective gel and lodge on a surface of the package cavity. Under certain conditions (e.g., at elevated temperatures, such as during a reflow process, and/or after exposure to significant changes in pressure within the external environment in which the sensor device is implemented), the moisture may transition to a gaseous state, producing bubbles at an interface between the gel and a surface within the package cavity. Those bubbles may thereafter migrate to the exposed surface of the gel. When the bubbles are sufficiently large and/or prolific, they may significantly deform the surface of the gel. The bubbles also may migrate to the surface of the sensor IC die. Either of these conditions, in turn, may produce a mechanical offset and, thus, inaccuracy in the sensor measurements (e.g., a false pressure output) that may be obtained by the device. In extreme cases, bubble-caused gel surface deformation may compromise the functionality of the sensor device.